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Reactions.— Add to a solution of the naphthol in water a few
drops of ferric chloride. A green colouration is produced, and
after a time a flocculent precipitate of dinaphthol, C^H^O^.

See also Reaction 6, p. 163.

/S-Naphthyl methyl ether.— Dissolve 3'6gramsiS-naphthol
in i2'5 c.c. 10 per cent, caustic soda solution, add 3 c.c. methyl
sulphate, warm the liquid gently and shake vigorously. In a
short time the naphthyl methyl ether separates as a solid mass.
The product is heated for ten minutes on the water-bath, a little
water is added, and the naphthyl ether filtered and washed with
water. It is crystallised from alcohol and deposits in lustrous
plates ; m. p. 70— -72°. The yield is theoretical. It may be
used for analysis by Zeisel's method.

Zeisel's Method. —The method consists in estimating
methoxyl or ethoxyl groups by decomposing the substance with
strong hydriodic acid and eliminating the alkyl group as alky!
iodide. The alkyl iodide is passed through an alcoholic solution
of silver nitrate, which decomposes the alkyl iodide and the
silver iodide is weighed.

The apparatus devised by W. H. Perkin, senior, is shown in
Fig. 83 (Proc. Chem. Soc., 1903, 19, 1370).
It consists of a distilling flask (100 c.c.) with a long neck ; lh«
distance between the bulb and side tube is about 20 cms. (8 ins. .
It is provided with an inlet tube which terminates above the
surface of the liquid and is attached at the other end with a
carbon dioxide Kipp and wash-bottle containing silver nitrate
solution to remove traces of hydrochloric acid or hydrogen sul-
phide. The side tube of the distilling flask is attached to two
small 100 c.c. Erlenmeyer flasks, provided with double-bored
rubber corks. The first bent tube which is attached to the side
tube of the distilling flask is cut off below the cork, the second
terminates just above the surface of the liquid in the first flask
and dips below the liquid in the second. The third or outlet
tube is bent at right angles and is cut off below the cork.
Thedistillingflaskisheated in a basin containing glycerol. The
first Erlenmeyer flask is charged with 20 c.c. alcoholic silver
nitrate, an/} the second with 15 c.c. of the same solution which
is prepared by dissolving 2 grams of fused silver nitrate in 5